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 Attaching Different Nets 

Last post Mon, Jan 13 2014 12:55 PM by Helen. 20 replies.
Started by Goblin59 27 Apr 2010 10:26 PM. Topic has 20 replies and 8481 views
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  • Sat, Dec 28 2013 11:39 PM

    Re: Attaching Different Nets Reply

    I have to think fabricators are calling with questions (and putting the job on hold) when shorted nets aren't specified in the fab drawing notes.

    If you design power systems with force/sense lines, it is faster/safer to check the sense location if the short is a physical component.  ATE testing of a 120-pin PMIC device with 16-30 different regulators for portable devices has lots of sense lines.  Ultimately, deliberate shorts have to be visible, controlled, and verified on the schematic/netlist level.

    MGCDesignArchitect has a "net alias" function allowing you to connect two nets together.  But, which net will get exported to layout as the other netname never leaves the schematic causes extra work (schematic pages are compiled in numerical order.  Net name assignment isn't random.  But, it may as well be.) Engineers have no easy way of finding where the designer put the sense line junction on a power net.

    Deliberate-short components can be safe and save time in some situations.  Fabricator seems to like running CAM on a board with zero shorts, then merge the shorting artwork.

    Our default template for fabrication drawings specifies merging short artwork after cam DRCs to copper artwork. It works for us. Our design review process focuses on a DRC report with zero errors, zero override.

    If we have to, we'll list the shorted nets on the fab drawing.

    • Post Points: 5
  • Mon, Jan 6 2014 9:51 AM

    • Poppy
    • Not Ranked
    • Joined on Fri, Feb 13 2009
    • North Wales, PA
    • Posts 13
    • Points 95
    Re: Attaching Different Nets Reply

     daltools has a large number of powerful Skill commands ( www.daltools.com )

    One of which is Net short (http://www.daltools.com/demo/NetShort/NetShort.mp4 )

    Mike Wilson

    • Post Points: 5
  • Mon, Jan 6 2014 1:47 PM

    Re: Attaching Different Nets Reply

    I don't know if this would be the ideal method, but I have shorted the board with static shape and waived the DRC then put a note on the tooling drawing stating that the two nets are shorted at certain location.

    This got me by from getting a call from the board houses.  I do understand the issue with this patch job, but it has worked for me when it was needed. 

    • Post Points: 20
  • Tue, Jan 7 2014 6:58 AM

    • mcatramb91
    • Top 75 Contributor
    • Joined on Thu, Jan 3 2013
    • Chelmsford, MA
    • Posts 101
    • Points 4,995
    Re: Attaching Different Nets Reply


    If you used a static shape to short between pins than you should consider adding the NET_SHORT property to one or both of the Pins to avoid having a DRC to waive.  The Value of the NET_SHORT property would contain both net names to be shorted separated by a colon ( GND:GND_PWR ) and it will only allow a short at those locations.  I have also added a single pin test point to the design so it could be easily placed anywhere that the short was desired.

    The one advantage of using the NET_SHORT property is that it will be reported in the header of the IPC-356 Netlist with the Pin and/or Via locations where the short occurs.  You could add the NET_SHORT property to one of the shapes to eliminate the DRC as well but it will not be reported in the IPC-356 Netlist because the netlist only contains Pin and Via information.

    I have used this process on many boards in the past without any issues.  Of course, it is always a good idea to include a note on the tooling drawing as well to avoid any fabrication delays.

    Hope this helps,
    Mike Catrambone

    • Post Points: 35
  • Wed, Jan 8 2014 9:24 AM

    Re: Attaching Different Nets Reply

    Thanks Mike. 

    I've used the net_short property on the shapes before and I didn't like how it could be shorted everywhere so I just waived the DRC instead, but this works much better for me.


    • Post Points: 5
  • Mon, Jan 13 2014 12:55 PM

    • Helen
    • Top 500 Contributor
    • Joined on Wed, Jul 23 2008
    • Posts 17
    • Points 165
    Re: Attaching Different Nets Reply

     In latest release you can attach PIN_SHORT property to your shorting device symbol and Packager will assign correct net_short properties to all pins in allegro.

    Remember to add .cpm directive:





    • Post Points: 5
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Started by Goblin59 at 27 Apr 2010 10:26 PM. Topic has 20 replies.